Conventionally, in printing plate making and medical fields, effluent generated by wet processing of image forming materials has been concerned from the ease of work. Recently, a decrease in the processing effluent has been strongly demanded from the viewpoint of environmental protection as well as saving of floor space. Accordingly, needed has been the development of techniques regarding light/heat sensitive photographic materials which can be subjected to efficient exposure employing a laser image setter as well as a laser imager and can form sharp and clear black-and-white images of high resolution.
As techniques to meet those requirements, thermally developable materials for preparing photographic images employing thermal development methods are disclosed in, for example, U.S. Pat. Nos. 3,152,904 and 3,457,075, and D. Morgan and B. Shely, "Thermally Processed Silver Systems" in "Imaging Processes and Materials", Neblette, 8th edition, edited by Sturge, V. Walworth, A Shepp, page 2, 1969.
The feature of these thermally developable materials is that images are formed by thermal development, generally at 80 to 140.degree. C. employing reducing agents incorporated into the photosensitive layer, and the fixing step is eliminated. However, in the above-cited thermally developable materials, image problems have tended to occur because normal image formation is locally hindered due to the presence of silver halide and organic silver coagula.
On the other hand, when silver halides or organic silver salts are forcibly disperse-pulverized by employing a homogenizer, problems occur in which fog increases, sensitivity decreases, and image quality deteriorated. Therefore, techniques have been demanded which are capable of yielding greater light sensitivity as well as higher density without an increase in the silver amount, while decreasing fog.